Miles Nadal, the outspoken chief executive of ad firm MDC Partners, wants his agencies to put their money where their mouths are.

Nadal is calling on his shops to become the private-equity firms of the advertising world by investing in brands or companies – raising outside capital if necessary to get in on the action.

Toronto-based MDC is not well known in the U.S. and is still a small fry compared to ad giants like Omnicom and WPP Group, but the company owns stakes in some of the hottest agencies around, including Crispin Porter + Bogusky.

“We’re prepared to put up capital,” Nadal said in an interview after sending a memo to his agency heads that hinted at his strategy. “We want to become the Goldman Sachs of marketing services.”

Facing shrinking fees and fed-up clients, Nadal is not the first to suggest changes in the way ad agencies get paid. More shops are working out revenue-sharing deals or taking equity stakes in lieu of the fees they normally charge.

Crispin, for instance, received a small equity stake in clothing company Haggar as part of its pay for providing marketing services.

But Nadal is more ambitious in that he wants MDC to court the private-equity firms that are snapping up troubled brands right and left and, in many cases, turning them around.

Crispin is credited with helping rescue the ailing company with a strange – some said creepy – mascot that attained a kind of cult status. The buyout firms took Burger King public in May, raising $425 million through the offering.

Nadal would like his agency to get in on the ground floor of such deals rather than collecting fees after the fact.

“We think private equity investors are going to play a much more active role in brands,” Nadal said. “The next time they buy Burger King, we’d like to be a co-investor.”

Nadal has his share of detractors for MDC’s uneven financial performance and corporate governance practices. It’s also no secret that he desires to run with the advertising big boys and is willing to gamble to grow fast.

Veteran ad execs caution that it can be risky for agencies with slim profit margins to put their own money into products and to forego fees.

But Nadal said he plans to leverage his track record of buying and investing in firms to cozy up to the private equity community. He’s also looking to raise capital that would allow MDC to identify its own opportunities and buy brands directly.